The present invention pertains to electrical circuits and circuit testers, and more particularly to circuits with ground fault circuit interrupters, circuit testers and methods for testing electrical circuits.
The modern electrical home has a plurality of circuits connected to a circuit box which is in turn connected to the line voltage. The National Electrical ode ("NEC") requires all such circuits to be protected from shorts by a circuit overload device such as a fuse or a circuit breaker. In recent years, the NEC required each circuit to be grounded and to have three-prong outlets. However, homes built prior to 1973 were not required by the NEC to have these grounded circuits, and most of those pre-1973 buildings are equipped with two-prong outlets and ungrounded electrical circuits.
Such electrical circuits, under certain circumstances, can cause severe shocks or even electrocution. As circuit overload devices, such as fuses and circuit breakers, only isolate a circuit from the line voltage at an appreciable number of amperes, the danger of electrocution and shock is always present in such circuits even when grounded. Circuit breakers will not detect low level current leakage under the breaker rating, i.e., under about 15 amperes, will not detect a faulty appliance, will not detect a neutral wire grounded to cold water piping downstream of the electrical panel, will not detect expose wiring, will not detect outlets and appliances in which the ground wire and the hot wire are reversed, will not detect more than one breaker feeding a circuit, will not detect a ground wire sharing more than one circuit, and will not detect circuits not grounded at the panel. All of these problems can occur in any building.
Whenever a person touches an appliance under a situation in which a battery ground is provided through the person, the current leakage will occur through the person, not through the ground wire and cause a shock. Whether or not the shock is safe or unsafe depends upon the amperage leaked through the person. Such shocks below five milliamperes are harmless. Five milliamperes is approximately the shock felt from static electricity in the carpet. Five to eight milliamperes, a severe shock sensation will occur. Eight to fifteen milliamperes, a painful shock that could result in death may occur. Fifteen to twenty milliamperes affects muscle control and the person being shocked cannot extricate himself from the circuit. Over 200 milliamperes, severe burns and heart failure occurs.
It is therefore highly desirable to provide an improved circuit using ground fault circuit interrupters which are resetable, on/off switches which will shut off upon sensing any current leakage in a circuit measuring more than 0.005 milliamperes in 1/40 of a second.
While ground fault circuit interrupters have been available since 1973, their use is still being explored. The 1990 edition of the NEC requires only limited ground fault interrupter protection for circuits in new construction in such areas as the kitchen, bath, garage, laundry, and outdoors. Ground fault interrupter code requirements are primarily for shock safety.
The 1993 NEC still does not require all circuits to be protected by ground fault circuit interrupters. Thus, many buildings have circuits which are unprotected by ground fault interrupters. Many of those circuits may leak current at dangerous levels. Ground fault interrupters also have a plurality of uses not heretofore realized.
It is therefore highly desirable to provide an improved circuit tester and method for testing circuits.
It is also highly desirable to provide an improved circuit tester and method for testing circuits to determine current leakage in amounts above 0.005 amperes.
It is also highly desirable to provide an improved circuit tester and method for testing circuits which detects not only current leakage, but approximate location that the current leakage is occurring such that the leakage can be repaired.
It is also highly desirable to provide an improved circuit tester and method which requires a minimum of knowledge by the operator such that it can be conveniently utilized by a building owner or handyman and not require trained electricians or electrical engineers.
It is also highly desirable to provide an improved circuit tester and method for testing circuits which is simple and inexpensive to manufacture.
It is also highly desirable to provide an improved circuit tester and method for testing circuits which is consistent with the NEC.
It is also highly desirable to provide an improved circuit with a ground fault circuit interrupter for new construction.
Finally, it is highly desirable to provide an improved circuit tester and method for testing circuits and an improved circuit which include all of the above features.